The present invention relates to vacuum impregnation of sintered materials with dry lubricant, preferably, vacuum impregnation of sintered bearings parts. More particularly, this invention is concerned with vacuum impregnation of bearings parts, so that a supply of a dry lubricant will be integrally contained therein.
It is known that finely divided metals may be sintered under appropriate conditions of heat and pressure to yield a porous structure that can be impregnated with a lubricant. This type of bearing has proved of utility in certain limited applications, but is generally found lacking in that the fugitive lubricant is not tightly held in the interstices of the sintered metal. As a result, the lubricant may bleed out of the bearing under no load conditions or may be extracted therefrom by centrifugal forces if the bearing is subjected to rotation. For this reason, it is generally necessary to provide means to replace the supply of lubricant in such self-lubricated bearings, either continuously or at predetermined intervals.
Metal bearings have also been lined with certain solid non-metallic substances that have low coefficient of friction and will serve as lubricants. Bearings of this type are, for example, those that are lined with low friction resinous materials such as polyethylene and polyamides. Under comparatively light loads these bearings have sometimes proved satisfactory, but they do not have the necessary wear resistance to permit their use under moderate to severe pressure-velocity conditions. Thus, their utility is limited.
A third type of self-lubricated bearing may be prepared by applying a layer of adhesive material to a metal substrate, contacting the adhesive layer with a finely divided absorptive resinous material, and causing the adhesive material to harden, whereby a layer of finely divided synthetic resinous material is bounded to at least the surface of said substrate. The metal substrate may be shaped into the form of a bearing either before or after the finely divided resinous material is applied to the surface. Such a bearing is described in U.S. Pat. No. 3,380,843.
Another similar process is described in U.S. Pat. No. 4,104,176. According to this patent there is applied to the surface of the bearing a matrix of closely spaced, solid discrete particles held together, not through the compaction and sintering of powder metallurgy, but with a bonding material disposed in the interstices between the particles. The bonding material only partially fills the interstices and leaves an interconnected uniform porosity sufficient to provide at the bearing surface the lubricant needed for a lubricant-impregnated bearing. The main disadvantage of the bearings according to these patents is that the fabrication of them is relatively complicated.